Cold rolled steel sheets having an improved press formability
A cold rolled steel sheet or plated steel sheet having an improved press formability as well as excellent phosphatability, resistance to galling and spot weldability is produced by controlling a surface roughness pattern of the steel sheet so as to satisfy a center-line average surface roughness of 0.3-2.0 .mu.m and a regularity parameter in at least one direction of not more than 0.25 defining the regularity of surface roughness.
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1. Field of the Invention
This invention relates to cold rolled steel sheets and plated steel sheets having considerably improved press formability, phosphatability, weldability and resistance to galling by controlling surface roughness pattern of steel sheet.
2. Related Art Statement
Drawable cold rolled steel sheets used for automobile panels, electric appliances, culinary equipments and so on are required to have an excellent deep drawability. In order to enhance the deep drawability, it is necessary that the steel sheet has high ductility (E1) and Lankford value (r-value) as mechanical properties. In fact, the drawing (particularly in the formation of automobile panel) is frequently combined with the flanging, so that work hardening index (n-value) becomes also important.
In the outer panel for the automobile, the finish feeling after painting is an important item directly connecting to the quality of the automobile itself in users.
Furthermore, the pretreatment for baking or phosphatability is important in the steel sheet for automobiles. That is, when the phosphatability is not good, sufficient baking property can not be ensured.
In the steel sheet for automobiles, it is also required to subject the present part to a spot welding, so that the spot weldability of steel sheet becomes important.
In the press forming, there may be caused the seizing between the steel sheet and the press mold, or a so-called galling phenomenon. Such a galling unfavorably causes the damage of the mold, considerable degradation of commercial value of the pressed parts and the like.
In the automobile industry, one-side surface treated steel sheets have hitherto been used as a body plate of an automobile exposed to severer corrosion environment, wherein the inner surface of the steel sheet is a plated or organic coating surface and the outer surface thereof is a cold rolled surface. Even in the outer surface of the body plate, however, rusting or blistering is caused due to the collision with gravels, pebbles and so on. Therefore, both-side surface plated steel sheets have lately been used as the body plate.
Since the steel sheet for automobile is subjected to various press forming prior to the assembling into the automobile body, it is required to have an excellent deep drawability. However, the galvanized steel sheets usually used for the automobile are apt to be seized to the press mold in the press forming due to the presence of galvanized coating as compared with the usual cold rolled steel sheet, and are poor in the deep drawability.
The investigations on deep drawing are made from two viewpoints of steel sheet and drawing technique. However, requirements for the steel sheet tend to become high-grade and deversified together with the accurate increase and complication of the product. Particularly, this tendency is strong in the cold rolled steel sheet for automobile.
For instance, plural pressed parts are spot-welded in the assembling of the vehicle body at the present. Therefore, it is strongly demanded to reduce the number of spot-welded points by oversizing the pressed part or making these pressed parts into one body. On the other hand, the car design becomes more complicated in compliance with the various needs, and consequently difficult molding parts increase in the usual cold rolled steel sheet. In order to satisfy these needs, it is necessary to use cold rolled steel sheets having an improved press formability as compared with the usual cold rolled steel sheet.
In the actual press forming, the mechanical properties (r-value, E1, n-value) of steel sheet have hitherto been used as an evaluation standard of press formability, but they are not still insufficient. For instance, the press formability is also largely influenced by the surface roughness of steel sheet, the lubricating oil and the like.
There are some well-known techniques showing an influence of surface roughness of steel sheet upon press formability and so on. For example, Plasticity and Work, Vol. 3, No. 14 (1962-3) discloses that when using a high viscosity lubricating oil, the drawability is most improved at the steel sheet surface roughness of about several .mu.m. On the other hand, Japanese Patent Application Publication No. 59-34,441 discloses that the appearance after painting and press formability are more improved by subjecting a cold rolled steel sheet to a skin pass rolling through a dull roll having a center-line average surface roughness of Ra=2.8 (.mu.m) and peak number of PPI=226 as a roll surface roughness.
These well-known techniques are excellent in view of the improvement of press formability, but have a drawback that the surface roughness of steel sheet should be controlled to a certain level.
In Japanese Patent laid open No. 54-97,527 is disclosed a method wherein a cold rolled steel sheet having an improved phosphatability can be produced by subjecting to a skin pass rolling through a roll having PPI=150 as a roll surface roughness. This method provides an excellent phosphatability but does not develop an effect on press formability. In general, the phosphatability is required for the steel sheet used in automobiles, and also the press formability and distinctness of image after painting (DOI) become necessarily important.
The aforementioned conventional techniques do not teach nor suggest a method of producing cold rolled steel sheets and plated steel sheets having an optional surface roughness (Ra, PPI) and excellent press formability, phosphatability, weldability and resistance to galling.
SUMMARY OF THE INVENTIONIt is therefore, an object of the invention to solve the above mentioned drawbacks of the conventional technique and to provide cold rolled steel sheets and plate steel sheets having improved press formability, phosphatability, weldability and resistance to galling by giving an orientation to a surface roughness pattern and controlling a center-line average surface roughness, a mean area ratio of convex portions measured at center plane of surface roughness, a mean area per one convex portion at center plane of surface roughness, a mean radius of convex portions measured at center plane of surface roughness and a mean radius of concave portions measured at center plane of surface roughness.
According to the invention, there are provided cold rolled steel sheets and plated steel sheets having an improved press formability, characterized in that the steel sheet has a surface roughness pattern satisfying a center-line average surface roughness (Ra, .mu.m) of 0.3-2.0 .mu.m and a regularity parameter (S) in at least one direction of not more than 0.25 showing a regularity of surface roughness represented by the following equations: ##EQU1## wherein Xi is a distance between peaks of convex portions at the surface of the steel sheet.
In a preferred embodiment of the invention, the surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr, .mu.m.sup.2) of 2,000-30,000.
In another embodiment of the invention, the surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr, .mu.m.sup.2) of 2,000-30,000 and at least one requirement selected from a product of center-line average surface roughness (Ra, .mu.m) and mean concave distance (Lmv, .mu.m) of not less than 50, a ratio of mean concave radius (Rmv, .mu.m) to mean convex radius (Rmp, .mu.m) of more than 1, and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention will be described with reference to the accompanying drawings, wherein:
FIG. 1 is a graph showing a relation between regularity parameter (S value) in surface roughness pattern and limit drawing ratio;
FIG. 2 is a graph showing a relation between product of center-line average surface roughness (Ra) and mean concave distance (Lmv) and phosphatability;
FIG. 3 is a graph showing a relation between mean area ratio of convex portions at center plane of surface roughness (SSr) and spot weldability or tensile sharing strength;
FIG. 4 is a graph showing a relation between ratio of mean concave radius (Rmv) to mean convex radius (Rmp) at center plane of surface roughness and resistance to galling;
FIGS. 5 and 6 show surface roughness patterns of steel sheets, respectively .
DESCRIPTION OF THE PREFERRED EMBODIMENTSThe invention will be described in detail with respect to results of studies resulting in the success of the invention.
Two cold rolled sheets of low carbon aluminum killed steel having a chemical composition shown in the following Table 1 were used as a steel to be tested.
TABLE 1
______________________________________
Steel
C Si Mn P S N Al
______________________________________
A 0.032 0.02 0.21 0.013 0.008 0.0037
0.045
B 0.002 0.01 0.12 0.008 0.004 0.0026
0.032
______________________________________
Each of the two test sheets was subjected to a skin pass rolling through a pair of rolls, at least one of which being subjected to a dulling through a laser (hereinafter referred to as a laser dulling), at a draft of 0.8%. In this case, the surface roughness pattern of the steel sheet after skin pass rolling was changed by varying the laser dulling process. The measured results are shown in FIG. 1, wherein S value is a measured value in the rolling direction of the steel sheet.
As seen from FIG. 1, the center-line average surface roughness (Ra) was about 1.2 .mu.m, while the limit drawing ratio was strongly dependent upon S value. The press formability was considerably improved at S.ltoreq.0.25.
Further, when the mean area per one convex portion at center plane of steel sheet SGr (.mu.m.sup.2) after skin pass rolling is limited to a range of 2,000 to 30,000, the press formability is further improved and also the distinctness of image is effectively improved.
Further, a relation between a product of centerline average surface roughness (Ra, .mu.m) after the skin pass rolling of the steel sheet and mean concave distance (Lmv, .mu.m) and a phosphatability was examined with respect to the steel B of Table 1 to obtain results as shown in FIG. 2. In this case, the draft in the skin pass rolling was 0.8% and S value was 0.18.
The phosphatability was evaluated by pin hole area ratio when the steel sheet was degreased, washed with water, phosphated and subjected to a pin hole test as mentioned later. Moreover, the phosphate treatment was carried out with BT 3112 made by Japan Perkerizing K.K., by adjusting to total acidity of 14.3 and free acidity of 0.5 and then spraying for 120 seconds.
Pin hole test:
A non-covered portion of phosphate crystal coating in the surface of the steel sheet was detected by sticking a filter paper impregnated with a reagent developing a color through reaction with iron ion to the steel sheet surface, which was numeralized as a pin hole area ratio by image analysis. As a standard on the evaluation of phosphatability, 1 is a case that the pin hole area ratio is less than 0.5%, 2 is a case that the ratio is 0.5-2%, 3 is a case that the ratio is 2-9%, 4 is a case that the ratio is 9-15%, and 5 is a case that the ratio is more than 15%. 1 and 2 show evaluation causing no problem in practical use.
As seen from FIG. 2, the phosphatability is largely dependent on Ra.times.Lmv and is considerably improved at Ra.times.Lmv.gtoreq.50.
Moreover, a relation between a mean area ratio of convex portions at center plane of surface roughness (SSr, %) and a spot weldability (or tensile shearing strength) was examined with respect to the steel B of Table 1 after the skin pass rolling to obtain results as shown in FIG. 3. In this case, the sheet gauge was 0.8 mm, the draft in the skin pass rolling was 0.8% and S value was 0.15.
The spot weldability was largely dependent upon SSr. The tensile shearing strength after spot welding was remarkably improved at SSr.gtoreq.45(%). As spot welding conditions, the welding time was 8 seconds, the pressing force was 190 kg and the welding current was 7,800 A.
And also, a relation between a ratio of mean concave radius (Rmv, .mu.m) to mean convex radius (Rmp, .mu.m) at center plane of surface roughness and a resistance to galling was examined with respect to the steel B of Table 1 after the skin pass rolling to obtain results as shown in FIG. 4. In this case, the draft in the skin pass rolling was 0.8% and S value was 0.16. As seen from FIG. 4, the resistance to mold dropping off is strongly dependent upon Rmv/Rmp and is considerably improved at Rmv/Rmp>1.
The inventors have made further studies on the basis of the above fundamental data, and found that cold rolled steel sheets and plated steel sheets having improved press formability, phosphatability, spot weldability and resistance to galling can be produced by controlling the production conditions as mentioned below.
At first, the surface roughness pattern of the steel sheet is most important.
Then, the regularity parameter S showing a regularity of surface roughness in the steel sheet according to the invention can be expressed by the following equations when a distance between peaks of convex portions on the steel sheet surface is Xi; ##EQU2##
The mean concave distance Lmv is expressed by the following equation in the surface roughness pattern shown in FIG. 5: ##EQU3##
Further, the mean convex radius Rmp and mean concave radius Rmv at center plane of surface roughness are expressed by the following equations in the surface roughness pattern shown in FIG. 6, respectively: ##EQU4## wherein Sp is an area of convex portion at center plane, Sv is an area of concave portion at center plane, np is number of convex portions at center plane and nv is number of concave portions at center plane.
According to the invention, the regularity parameter S is required to satisfy S.ltoreq.0.25 in at least one direction. When S>0.25, the excellent press formability can not be obtained. In the conventional cold rolled steel sheet, S value is about 0.3-0.5.
The center-line average surface roughness (Ra) of the steel sheet is essential to be within a range of 0.3-2.0 .mu.m. When Ra<0.3 .mu.m, the excellent press formability can not be obtained, while when Ra>2.0 .mu.m, the distinctness of image substantially equal to that of the usually used steel sheet can not be obtained.
The mean area per one convex portion at center plane of surface roughness SGr (.mu.m.sup.2) is necessary to be within a range of 2,000-30,000. When SGr<2,000, the distinctness of image substantially equal to that of the usually used steel sheet can not be obtained, while when SGr>30,000, the press formability is degraded.
Further, the center-line average surface roughness Ra (.mu.m) and mean concave distance Lmv (.mu.m) are necessary to satisfy a relation of Ra.times.Lmv.gtoreq.50. When Ra.times.Lmv<50, the excellent phosphatability can not be obtained.
The mean area ratio of convex portion at center plane of surface roughness SSr(%) is necessary to be not less than 45%. When SSr<45%, the excellent spot weldability can not be obtained.
Moreover, the mean convex radius Rmp (.mu.m) and mean concave radius Rmv (.mu.m) at center plane of surface roughness are necessary to satisfy a relation of Rmv/Rmp>1. When Rmv/Rmp.ltoreq.1, the desired resistance to galling can not be obtained.
In order to provide the regular surface roughness pattern satisfying the above requirements on the steel sheet, the surface roughness pattern of skin pass roll should necessarily be regular. For this purpose, the skin pass roll is subjected to a discharge dulling process, a laser dulling process or a shot blast process using a specially formed grid.
According to the invention, the kind of lubricating oil and the pressing conditions are optional.
The effect of the regular surface roughness pattern of steel sheet according to the invention is considered to make good the lubrication condition resulted from the fact that the lubricating oil pooled in concave portions on the steel sheet surface is equally supplied to convex portions. Furthermore, it is considered that the friction state between the steel sheet and the press mold is well improved owing to the fact that metal-contacting parts of convex portions are regularly present on the steel sheet surface.
As to the phosphatability, the surface roughness pattern of the steel sheet is considered to influence the formation of phosphate crystal nucleus, the detail of which is not clear.
Further, it is considered that the spot weldability is improved at SSr.gtoreq.45% because the bonding property between steel sheet surfaces in the spot welding is good.
As regards the resistance to galling, it is considered that iron powders produced in the press working are apt to flow into concave portions at Rmv/Rmp>1 and mitigate the seizing phenomenon between the steel sheet and the press mold.
The invention will be described in detail with reference to the following examples.
A steel slab having a chemical composition as shown in the following Table 2, 5, 8, 11, 14, 17, 20, 23 or 26 was produced by a converter-continuous casting process, soaked by heating at 1,250.degree. C., and subjected to rough rolling-finish rolling to obtain a hot rolled steel sheet of 3.2 mm in thickness. The resulting steel sheet was pickled, cold rolled to a thickness of 0.8 mm, and subjected to a continuous annealing (soaking temperature: 750.degree.-850.degree. C.) and further to a skin pass rolling (draft: 0.8%).
In this case, a roll dulled by shot blast or laser process was used as a skin pass roll.
The surface roughness of the steel sheet was measured in an L-direction to obtain center-line average surface roughness Ra, ten-point average roughness Rz and regularity parameter S. Further, the mean area per one convex portion at center plane of surface roughness SGr, mean area ratio of convex portions SSr, mean convex radius Rmp and mean concave radius Rmv were determined by using a three-dimensional surface roughness measuring meter.
The tensile properties were measured by using a No. 5 test piece defined in JIS Z 2201. The Lankford value was measured by a three-point method in L-direction (rolling direction), C-direction (90.degree. to rolling direction) and D-direction (45.degree. to rolling direction) under a tensile prestrain of 15%, from which r-value was calculated according to an equation of r=(r.sub.L +r.sub.C +2r.sub.D)/4.
The limit drawing ratio (L.D.R.) was calculated according to the following equation by measuring a maximum diameter (D.sub.O max) of sheet capable of deep drawing in a mold with a punch having a diameter (dp) of 32 mm: ##EQU5## As the drawing conditions, the drawing speed was 1 mm/sec and the lubricating oil was a rust preventive oil (oil type).
Moreover, the plated steel sheet was produced by subjecting the cold rolled steel sheet to a skin pass rolling (draft: 0.8%) and further to zinc electroplating, Zn-Ni alloy electroplating or Zn-Fe alloy electroplating, or by subjecting a cold rolled steel sheet to a zinc hot dipping and further to a skin pass rolling (draft: 0.8%).
EXAMPLE 1Table 2 shows a chemical composition of a cold rolled steel sheet used, and Table 3 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 3, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0 and S.ltoreq.0.25 exhibit an excellent press formability as compared with the comparative steel sheets.
TABLE 2
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.035 0.02 0.18 0.012 0.007
0.0038
0.046
--
D 0.002 0.01 0.11 0.007 0.004
0.0029
0.030
--
E 0.002 0.01 0.12 0.007 0.005
0.0023
0.031
Ti: 0.028
F 0.003 0.02 0.13 0.008 0.004
0.0026
0.033
Nb: 0.015
G 0.002 0.01 0.09 0.006 0.003
0.0022
0.028
Ti: 0.014
Nb: 0.008
______________________________________
TABLE 3
__________________________________________________________________________
Surface
Roll roughness
Properties
dulling
Ra YS TS El
Steel
method
(.mu.m)
S value
(Kg/mm.sup.2)
(Kg/mm.sup.2)
(%)
-r
L.D.R.
Remarks
__________________________________________________________________________
C shot blast
1.2
0.35 20 35 44 1.4
2.12
Comparative
Example
C shot blast
1.3
0.41 20 35 44 1.4
2.09
Comparative
Example
C laser
1.1
0.12 20 35 44 1.4
2.31
Example
D laser
1.3
0.23 15 28 50 2.0
2.48
Example
D shot blast
1.2
0.50 15 28 50 2.0
2.28
Comparative
Example
E laser
1.9
0.21 16 29 52 2.2
2.51
Example
F laser
2.0
0.18 17 30 50 2.1
2.53
Example
G shot blast
0.6
0.38 16 29 51 2.2
2.31
Comparative
Example
G laser
0.7
0.08 16 29 51 2.2
2.53
Example
__________________________________________________________________________
EXAMPLE 2
Table 5 shows a dulling method for skin pass roll, kind of plating and surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 4. As seen from Table 5, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0 and S.ltoreq.0.25 exhibit an excellent press formability compared with the comparative steel sheets.
TABLE 4
______________________________________
C Si Mn P S N Al Ti
______________________________________
Steel
0.002 0.01 0.09 0.007 0.008
0.0022
0.064 0.041
______________________________________
TABLE 5
__________________________________________________________________________
Surface rough-
Deep
Roll ness of plated
draw-
dulling steel sheet
ability
method
Kind of plating
Ra (.mu.m)
S value
(L.D.R.)
__________________________________________________________________________
Example
laser
Zn electroplating
1.2 0.20
2.31
Example
laser
Zn--Ni alloy electroplating
1.5 0.15
2.33
Example
laser
Zn--Fe alloy electroplating
1.1 0.18
2.28
Example
laser
Zn hot dipping
0.8 0.09
2.34
(after
plating)
Example
laser
Zn electroplating
1.3 0.16
2.27
Example
laser
Zn electroplating
1.4 0.08
2.22
Comparative
shot blast
Zn electroplating
1.2 0.32
2.07
Example
Comparative
shot blast
Zn--Fe alloy electroplating
1.2 0.29
2.10
Example
__________________________________________________________________________
EXAMPLE 3
Table 6 shows a chemical composition of a cold rolled steel sheet used, and Table 7 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 7, the cold rolled steel sheets according to the invention satisfying 0.3.times.Ra.ltoreq.2.0, S.ltoreq.0.25 and 2,000.ltoreq.SGr.ltoreq.30,000 exhibit excellent press formability and distinctness of image after painting as compared with the comparative steel sheets.
TABLE 6
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.036 0.02 0.22 0.016 0.007
0.0044
0.047
--
D 0.002 0.01 0.16 0.009 0.004
0.0029
0.029
--
E 0.004 0.01 0.12 0.011 0.004
0.0031
0.031
Ti: 0.035
F 0.003 0.01 0.15 0.012 0.003
0.0033
0.032
Nb: 0.021
G 0.002 0.01 0.10 0.008 0.004
0.0028
0.028
Ti: 0.016
Nb: 0.009
______________________________________
TABLE 7
__________________________________________________________________________
Surface
Roll roughness Properties
dulling
Ra SGr YS TS El
Steel
method
(.mu.m)
S value
(.mu.m.sup.2)
(kg/mm.sup.2)
(kg/mm.sup.2)
(%)
-r
L.D.R.
DOI
Remarks
__________________________________________________________________________
C shot blast
1.2
0.33
1640
18 34 44 1.2
2.05
85 Comparative
Example
C laser
1.1
0.19
3150
18 34 44 1.2
2.31
96 Example
C laser
1.2
0.16
2120
18 34 44 1.2
2.35
95 Example
D laser
1.6
0.15
2530
15 28 51 1.8
2.49
95 Example
D shot blast
1.7
0.41
1230
15 28 51 1.8
2.33
82 Comparative
Example
E shot blast
0.8
0.28
1850
16 29 52 1.9
2.34
86 Comparative
Example
E laser
0.9
0.08
2430
16 29 52 1.9
2.58
94 Example
F laser
1.2
0.20
3960
16 28 50 2.0
2.51
97 Example
F shot blast
1.3
0.31
1090
16 28 50 2.0
2.31
81 Comparative
Example
G shot blast
3.1
0.36
1810
17 30 49 1.9
2.29
87 Comparative
Example
G laser
2.0
0.12
2630
17 30 49 1.9
2.52
95 Example
G laser
3.0
0.18
31510
17 30 49 1.9
2.21
88 Comparative
Example
__________________________________________________________________________
EXAMPLE 4
Table 9 shows a dulling method for sking pass roll, kind of plating and surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 8. As seen from Table 9, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25 and 2,000.ltoreq.SGr.ltoreq.30,000 exhibit excellent press formability and distinctness of image after painting as compared with the comparative steel sheets.
TABLE 8
__________________________________________________________________________
C Si Mn P S N Al Ti Nb B
__________________________________________________________________________
Steel
0.002
0.01
0.11
0.008
0.002
0.0028
0.052
0.014
0.008
0.009
__________________________________________________________________________
TABLE 9
__________________________________________________________________________
Surface roughness
of plated Deep
Roll steel sheet
draw-
dulling Ra SGr ability
method
Kind of plating
(.mu.m)
S value
(.mu.m.sup.2)
(L.D.R.)
DOI
__________________________________________________________________________
Example
laser
Zn electroplating
1.1
0.20
3210
2.30
95
Example
laser
Zn--Ni alloy electroplating
1.6
0.16
2640
2.32
93
Example
laser
Zn--Fe alloy electroplating
1.2
0.18
2330
2.28
96
Example
laser
Zn hot dipping
0.9
0.09
2560
2.33
94
(after
plating)
Example
laser
Zn electroplating
1.3
0.15
15630
2.26
96
Example
laser
Zn electroplating
1.2
0.08
28340
2.22
97
Comparative
shot blast
Zn electroplating
1.2
0.34
1540
2.05
83
Example
Comparative
shot blast
Zn--Ni alloy electroplating
3.0
0.33
1910
2.25
86
Example
Comparative
shot blast
Zn--Fe alloy electroplating
1.2
0.28
1008
2.08
82
Example
Comparative
laser
Zn hot dipping
2.9
0.21
32620
2.10
86
Example
(after
plating)
__________________________________________________________________________
EXAMPLE 5
Table 10 shows a chemical composition of a cold rolled steel sheet used, and Table 11 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 11, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000 and Ra.times.Lmv.gtoreq.50 exhibit excellent press formability, distinctness of image after painting and phosphatability as compared with the comparative steel sheets.
TABLE 10
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.034 0.02 0.16 0.011 0.006
0.0035
0.042
--
D 0.002 0.01 0.11 0.008 0.004
0.0028
0.035
--
E 0.002 0.01 0.12 0.007 0.003
0.0026
0.036
Ti: 0.022
F 0.003 0.01 0.11 0.009 0.004
0.0025
0.036
Nb: 0.014
G 0.002 0.01 0.08 0.008 0.005
0.0027
0.037
Ti: 0.013
Nb: 0.009
______________________________________
TABLE 11
__________________________________________________________________________
Properties
Roll Surface roughness Phos-
dulling
Ra Lmv
SGr YS TS El phat-
Steel
method
(.mu.m)
S value
(.mu.m)
(.mu.m.sup.2)
(kg/mm.sup.2)
(kg/mm.sup.2)
(%)
-r
L.D.R.
ability
DOI
Remarks
__________________________________________________________________________
C shot blast
1.4
0.36
25.6
1630
20 35 45 1.4
2.09
5 84 Comparative
Example
C shot blast
1.3
0.44
33.7
2420
20 35 45 1.4
2.06
4 88 Comparative
Example
C laser
1.5
0.20
50.6
3940
20 35 45 1.4
2.36
1 96 Example
D laser
1.9
0.16
70.4
11420
15 28 52 1.9
2.51
1 97 Example
D shot blast
2.3
0.35
19.6
1360
15 28 52 1.9
2.31
4 83 Comparative
Example
E shot blast
1.3
0.32
30.2
2650
16 29 52 2.1
2.33
5 88 Comparative
Example
E laser
1.2
0.06
46.6
3380
16 29 52 2.1
2.58
1 95 Example
F laser
1.8
0.21
30.6
2160
17 30 50 2.0
2.55
1 94 Example
F shot blast
1.7
0.41
12.1
1830
17 30 50 2.0
2.29
5 82 Comparative
Example
G shot blast
0.7
0.30
46.3
7860
16 29 51 2.2
2.30
5 86 Comparative
Example
G laser
0.8
0.19
65.4
16430
16 29 51 2.2
2.56
2 97 Example
__________________________________________________________________________
EXAMPLE 6
Table 13 shows a dulling method for sking pass roll, kind of plating the surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 12. As seen from Table 13, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000 and Ra.times.Lmv.gtoreq.50 exhibit excellent press formability, distinctness of image after painting and phosphatability as compared with the comparative steel sheets.
TABLE 12
______________________________________
C Si Mn P S N Al Ti Nb
______________________________________
Steel
0.001 0.01 0.08 0.007
0.003
0.0029
0.051
0.019
0.006
______________________________________
TABLE 13
__________________________________________________________________________
Surface roughness of
Deep
Roll plated steel sheet
draw- Phos-
dulling Ra SGr Lmv ability
phat-
method
Kind of plating
(.mu.m)
S value
(.mu.m.sup.2)
(.mu.m)
(L.D.R.)
DOI
ability
__________________________________________________________________________
Example
laser
Zn electroplating
1.2
0.21 3240
51.2
2.30 95 1
Example
laser
Zn--Ni alloy electroplating
1.6
0.15 2730
33.6
2.32 93 1
Example
laser
Zn--Fe alloy electroplating
1.1
0.19 2310
47.4
2.28 96 1
Example
laser
Zn hot dipping
0.8
0.09 2430
63.4
2.33 91 1
(after
plating)
Example
laser
Zn electroplating
1.4
0.16 15600
38.2
2.26 96 1
Example
laser
Zn electroplating
1.2
0.09 27410
44.1
2.22 97 1
Comparative
shot blast
Zn electroplating
1.1
0.34 1530
41.6
2.05 83 5
Example
Comparative
shot blast
Zn--Ni alloy electroplating
3.1
0.33 1820
14.8
2.25 86 4
Example
Comparative
shot blast
Zn--Fe alloy electroplating
1.3
0.29 1010
35.2
2.08 82 5
Example
__________________________________________________________________________
EXAMPLE 7
Table 14 shows a chemical composition of a cold rolled steel sheet used, and Table 15 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 15, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000 and Rmv/Rmp>1 exhibit excellent press formability, distinctness of image after painting and resistance to galling as compared with the comparative steel sheets.
TABLE 14
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.035 0.02 0.21 0.019 0.008
0.0038
0.045
--
D 0.003 0.02 0.18 0.009 0.006
0.0022
0.039
B:0.002
E 0.002 0.01 0.16 0.008 0.004
0.0021
0.036
Ti:0.029
F 0.002 0.01 0.17 0.010 0.005
0.0019
0.032
Nb:0.012
G 0.002 0.02 0.12 0.008 0.003
0.0026
0.037
Ti:0.008
Nb:0.011
______________________________________
TABLE 15
__________________________________________________________________________
Properties
Roll Surface roughness Resist-
dulling
Ra Rmv/
SGr
YS TS El ance to
Steel
method
(.mu.m)
S value
Rmp (.mu.m)
(kg/mm.sup.2)
(kg/mm.sup.2)
(%)
r L.D.R.
galling
DOI
Remarks
__________________________________________________________________________
C shot blast
1.2
0.36 0.83
2860
19 34 46
1.3
2.08
5 82 Comparative
Example
C shot blast
1.3
0.34 0.88
1690
19 34 46
1.3
2.06
5 83 Comparative
Example
C laser
1.2
0.19 1.54
2790
19 34 46
1.3
2.33
1 95 Example
D shot blast
1.9
0.29 0.92
1880
15 28 52
1.8
2.32
4 84 Comparative
Example
D laser
1.8
0.20 1.23
3820
15 28 52
1.8
2.58
1 96 Example
E laser
1.6
0.18 1.32
2820
16 29 50
2.1
2.55
1 95 Example
E shot blast
1.5
0.39 0.73
1560
16 29 50
2.1
2.39
5 83 Comparative
Example
F shot blast
0.8
0.35 0.69
1840
17 30 51
2.0
2.33
5 84 Comparative
Example
F laser
0.9
0.22 1.12
7540
17 30 51
2.0
2.52
2 97 Example
G laser
1.5
0.08 1.29
5520
16 29 50
2.2
2.56
1 95 Example
G shot blast
1.6
0.30 0.82
1860
16 29 50
2.2
2.29
5 84 Comparative
Example
__________________________________________________________________________
EXAMPLE 8
Table 17 shows a dulling method for sking pass roll, kind of plating and surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 16. As seen from Table 17, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000 and Rmv/Rmp>1 exhibit excellent press formability, distinctness of image after painting and resistance to galling as compared with the comparative steel sheets.
TABLE 16
______________________________________
C Si Mn P S N Al Ti Nb
______________________________________
Steel
0.002 0.02 0.12 0.009
0.004 0.0019
0.061
0.026
0.011
______________________________________
TABLE 17
__________________________________________________________________________
Surface roughness of
Deep
Roll plated steel sheet
draw-
Resist-
dulling Ra Rmv/
SGr ability
ance to
method
Kind of plating
(.mu.m)
S value
Rmp (.mu.m.sup.2)
(L.D.R.)
galling
DOI
__________________________________________________________________________
Example
laser
Zn electroplating
1.2
0.15 1.51
2210
2.26 1 94
Example
laser
Zn electroplating
1.1
0.16 1.12
2340
2.34 1 94
Example
laser
Zn electroplating
1.2
0.19 1.65
3420
2.25 1 96
Example
laser
Zn electroplating
1.1
0.11 1.13
3300
2.32 1 95
Example
laser
Zn electroplating
1.3
0.20 1.61
2380
2.31 1 94
Example
laser
Zn--Ni alloy electroplating
1.3
0.17 1.32
4210
2.28 1 94
Example
laser
Zn--Fe alloy electroplating
1.2
0.09 1.23
3150
2.26 1 95
Example
laser
Zn hot dipping
0.9
0.13 1.20
2440
2.33 2 95
(after
plating)
Comparative
shot blast
Zn electroplating
1.3
0.35 0.89
1890
2.16 4 75
Example
Comparative
shot blast
Zn electroplating
1.3
0.42 0.98
2240
2.07 3 70
Example
Comparative
shot blast
Zn electroplating
1.1
0.38 0.86
1830
2.03 5 85
Example
Comparative
shot blast
Zn electroplating
1.1
0.29 0.75
2540
2.05 5 88
Example
Comparative
shot blast
Zn electroplating
1.4
0.34 0.81
3220
2.05 5 81
Example
Comparative
shot blast
Zn--Ni alloy electroplating
1.4
0.41 0.69
1850
2.01 5 80
Example
Comparative
shot blast
Zn--Fe alloy electroplating
1.3
0.28 0.93
2110
2.00 5 82
Example
Comparative
shot blast
Zn hot dipping
1.2
0.36 0.86
3120
2.09 5 83
Example
(after
plating)
__________________________________________________________________________
EXAMPLE 9
Table 18 shows a chemical composition of a cold rolled steel sheet used, and Table 19 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 19, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting and spot weldability as compared with the comparative steel sheets.
TABLE 18
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.033 0.02 0.20 0.013 0.007
0.0041
0.043
--
D 0.002 0.01 0.09 0.009 0.005
0.0026
0.029
--
E 0.003 0.01 0.12 0.011 0.003
0.0029
0.031
Ti:0.033
F 0.002 0.01 0.15 0.007 0.004
0.0031
0.028
Nb:0.013
G 0.004 0.01 0.13 0.010 0.003
0.0025
0.033
Ti:0.009
Nb:0.010
______________________________________
TABLE 19
__________________________________________________________________________
Properties
Tensile
Roll Surface roughness shearing
dulling
Ra SSr SGr YS TS El force
Steel
method
(.mu.m)
S value
(%) (.mu.m.sup.2)
(kg/mm.sup.2)
(kg/mm.sup.2)
(%)
r L.D.R.
(kg/mm.sup.2)
DOI
Remarks
__________________________________________________________________________
C shot blast
1.6
0.36 42 2820
19 35 45
1.3
2.08
353 81 Comparative
Example
C shot blast
1.5
0.33 33 3660
19 35 45
1.3
2.05
341 84 Comparative
Example
C laser
1.6
0.19 56 5420
19 35 45
1.3
2.35
482 95 Example
D shot blast
1.2
0.41 39 1220
15 28 52
1.9
2.31
342 82 Comparative
Example
D laser
1.1
0.22 62 6930
15 28 52
1.9
2.51
452 96 Example
E shot blast
0.9
0.32 41 2860
16 28 51
2.1
2.33
351 84 Comparative
Example
E laser
0.8
0.09 48 11220
16 28 51
2.1
2.59
446 97 Example
F laser
1.2
0.11 51 1820
16 29 50
2.0
2.53
449 92 Comparative
Example
F shot blast
1.3
0.29 40 2290
16 29 50
2.0
2.35
340 83 Comparative
Example
G laser
0.5
0.23 49 2290
17 30 50
2.1
2.50
445 95 Example
G shot blast
0.6
0.43 37 5230
17 30 50
2.1
2.31
338 84 Comparative
Example
__________________________________________________________________________
EXAMPLE 10
Table 21 shows a dulling method for sking pass roll, kind of plating and surface rougness and properties of the plated steel sheet having a chemical composition as shown in Table 20. As seen from Table 21, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting and spot weldability as compared with the comparative steel sheets.
TABLE 20
______________________________________
C Si Mn P S N Al Ti
______________________________________
Steel
0.002 0.02 0.09 0.010 0.008
0.0022 0.043
0.044
______________________________________
TABLE 21
__________________________________________________________________________
Surface roughness of
Tensile
Deep
Roll plates steel sheet shearing
draw-
dulling Ra Rz SSr SGr force
ability
method
Kind of plating
(.mu.m)
(.mu.m)
S value
(%) (.mu.m.sup.2)
(kg/mm.sup.2)
(L.D.R.)
DOI
Remarks
__________________________________________________________________________
Example
laser
Zn electroplating
1.9
10.0
0.21 48 2980
443 2.21 95
Example
laser
Zn--Fe alloy electroplating
2.0
10.4
0.20 52 3380
451 2.23 94
Example
laser
Zn electroplating
0.5
0.86
0.16 49 12500
431 2.21 97
Example
laser
Zn electroplating
0.4
1.24
0.18 56 6850
429 2.20 95
Example
laser
Zn electroplating
1.1
5.0
0.12 61 5120
440 2.30 95
Example
laser
Zn--Ni alloy electroplating
1.3
5.9
0.23 48 4280
451 2.21 94
Example
laser
Zn hot dipping
1.1
4.4
0.15 50 3860
428 2.24 93
(after
plating)
Comparative
shot blast
Zn electroplating
2.1
9.5
0.34 42 1230
382 2.05 67
Example
Comparative
shot blast
Zn electroplating
0.2
0.8
0.30 43 2890
336 2.02 73 reskin
Example pass
after
plating
Comparative
shot blast
Zn--Ni alloy electroplating
1.2
5.4
0.35 38 3340
354 2.03 68
Example
Comparative
shot blast
Zn--Fe alloy electroplating
0.6
3.0
0.38 36 2140
339 2.05 68
Example
Comparative
shot blast
Zn hot dipping
1.2
4.8
0.40 40 2290
368 2.00 65
Example
(after
plating)
__________________________________________________________________________
EXAMPLE 11
Table 22 shows a chemical composition of a cold rolled steel sheet used, and Table 23 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 23, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Ra.times.Lmv.gtoreq.50 and Rmv/Rmp>1 exhibit excellent press formability, distinctness of image after painting, phosphatability and resistance to galling as compared with the comparative steel sheets.
TABLE 22
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.035 0.03 0.24 0.019 0.009
0.0034
0.045
--
D 0.003 0.02 0.18 0.009 0.006
0.0022
0.039
Ti:0.024
Nb:0.009
B:0.0009
E 0.002 0.01 0.16 0.008 0.004
0.0021
0.036
Ti:0.038
______________________________________
TABLE 23
__________________________________________________________________________
Properties
Roll Surface roughness Resist-
Phos-
dulling
Ra Rmv/
Lmv
SGr YS TS El ance to
phat-
Steel
method
(.mu.m)
S value
Rmp (.mu.m)
(.mu.m.sup.2)
(kg/mm.sup.2)
(kg/mm.sup.2)
(%)
r L.D.R.
galling
ability
DOI
__________________________________________________________________________
C shot blast
1.2
0.33 0.82
39.2
1790
19 35 47
1.3
2.06
5 4 84 Compar-
ative
Example
C shot blast
1.3
0.31 0.86
32.1
1090
19 35 47
1.3
2.05
5 5 83 Compar-
ative
Example
C laser
1.2
0.16 1.53
116.8
4580
19 35 47
1.3
2.36
1 1 97 Example
D shot blast
0.7
0.27 0.91
14.8
210
16 29 51
1.9
2.34
4 5 82 Compar-
ative
Example
D laser
0.8
0.22 1.22
66.3
2320
16 29 51
1.9
2.59
1 1 96 Example
E laser
1.6
0.16 1.33
83.2
3070
16 28 50
2.1
2.57
1 1 97 Example
E shot blast
1.5
0.36 0.76
18.6
470
16 28 50
2.1
2.46
5 4 82 Compar-
ative
Example
__________________________________________________________________________
EXAMPLE 12
Table 25 shows a dulling method for sking pass roll, kind of plating and surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 24. As seen from Table 25, the plates steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Ra.times.Lmv.gtoreq.50 and Rmv/Rmp>1 exhibit excellent press formability, distinctness of image after painting, phosphatability and resistance to galling as compared with the comparative steel sheets.
TABLE 24
______________________________________
C Si Mn P S N Al Ti Nb
______________________________________
Steel
0.002 0.01 0.10 0.007
0.005 0.0018
0.051
0.031
0.006
______________________________________
TABLE 25
__________________________________________________________________________
Surface roughness of Deep
Roll plated steel sheet draw-
Resist-
Phos-
dulling Ra Lmv
SGr ability
ance to
phat-
method Kind of plating
(.mu.m)
S value
Rmv/Rmp
(.mu.m)
(.mu.m.sup.2)
(L.D.R.)
galling
DOI
ability
__________________________________________________________________________
Example
laser
Zn electroplating
1.3
0.16 1.24 68.3
2380
2.26 1 93 1
Example
laser
Zn electroplating
1.1
0.19 1.15 75.0
3340
2.25 1 96 1
Example
laser
Zn electroplating
1.3
0.21 1.33 79.8
2830
2.31 1 94 1
Example
laser
Zn--Fe alloy
1.1
0.09 1.23 70.2
2560
2.24 1 95 1
electroplating
Compar-
shot blast
Zn electroplating
1.4
0.36 0.76 33.8
1550
2.06 5 75 4
ative
Example
Compar-
shot blast
Zn electroplating
1.2
0.38 0.86 37.2
1470
2.03 5 85 5
ative
Example
Compar-
shot blast
Zn--Ni alloy
1.4
0.41 0.69 31.2
1610
2.05 5 80 5
ative electroplating
Example
__________________________________________________________________________
EXAMPLE 13
Table 26 shows a chemical composition of a cold rolled steel sheet used, and Table 27 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 27, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Ra.times.Lmv.gtoreq.50 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting, phosphatability and spot weldability as compared with the comparative steel sheets.
TABLE 26
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.036 0.02 0.21 0.012 0.007
0.0038
0.046
--
D 0.002 0.01 0.20 0.005 0.004
0.0029
0.030
Ti: 0.0022
Nb: 0.009
B: 0.0008
E 0.002 0.01 0.12 0.004 0.005
0.0023
0.031
Ti: 0.033
______________________________________
TABLE 27
__________________________________________________________________________
Properties
Tensile
Roll Surface roughness shearing Phos-
dulling
Ra S SSr
SGr Lmv
YS TS El force phat-
Steel
method
(.mu.m)
value
(%)
(.mu.m.sup.2)
(.mu.m)
(kg/mm.sup.2)
(kg/mm.sup.2)
(%)
.sup.-r
L.D.R.
(kg/mm.sup.2)
DOI
ability
Remarks
__________________________________________________________________________
C shot blast
1.6
0.34
41 340
30.1
19 34 45
1.3
2.02
352 82 4 Compar-
ative
Example
C shot blast
1.5
0.32
44 430
29.8
19 34 45
1.3
2.03
340 80 5 Compar-
ative
Example
C laser
1.6
0.19
55 2770
48.6
19 34 45
1.3
2.33
486 96 1 Example
D shot blast
1.2
0.42
39 480
38.6
15 28 51
1.9
2.32
341 83 5 Compar-
ative
Example
D laser
1.1
0.21
61 4480
48.3
15 28 51
1.9
2.53
454 97 1 Example
E shot blast
0.9
0.33
42 1040
50.2
16 28 52
2.2
2.34
352 84 5 Compar-
ative
Example
E laser
0.8
0.10
48 3580
73.1
16 28 52
2.2
2.56
446 96 1 Example
__________________________________________________________________________
EXAMPLE 14
Table 29 shows a dulling method for sking pass roll, kind of plating and surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 28. As seen from Table 29 the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Ra.times.Lmv.gtoreq.50 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting, phosphatability and spot weldability as compared with the comparative steel sheets.
TABLE 28
______________________________________
C Si Mn P S N Al Ti Nb
______________________________________
Steel
0.002 0.02 0.09 0.009
0.003
0.0014
0.063
0.013
0.012
______________________________________
TABLE 29
__________________________________________________________________________
Surface roughness of
Deep Tensile
Roll plated steel sheet draw- Phos-
shearing
dulling Ra SSr
Lmv
SGr ability phat
force
method Kind of plating
(.mu.m)
S value
(%)
(.mu.m)
(.mu.m.sup.2)
(L.D.R.)
DOI
ability
(kg/mm.sup.2)
Remarks
__________________________________________________________________________
Example
laser
Zn electroplating
2.0
0.16 48 60.4
2440
2.29 94 1 453
Example
laser
Zn electroplating
0.6
0.16 51 90.2
6920
2.29 97 1 482
Example
laser
Zn electroplating
0.8
0.18 62 64.3
8640
2.35 95 2 476
Example
laser
Zn--Ni alloy
1.4
0.24 54 45.2
2210
2.21 92 1 473
electroplating
Example
laser
Zn hot dipping
1.2
0.16 49 53.6
2080
2.26 93 1 452
(after
plating)
Compar-
shot blast
Zn electroplating
2.1
0.35 44 22.8
250
2.05 67 5 362
ative
Example
Compar-
shot blast
Zn electroplating
1.2
0.33 43 38.4
660
2.02 73 4 373 reskin
ative pass
Example after
plating
Compar-
shot blast
Zn electroplating
0.8
0.41 42 58.3
1400
2.05 70 5 381 reskin
ative pass
Example after
plating
__________________________________________________________________________
EXAMPLE 15
Table 30 shows a chemical composition of a cold rolled steel sheet used, and Table 31 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 31, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.245, 2,000.ltoreq.SGr.ltoreq.30,000, Rmv/Rmp>1 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting, resistance to galling and spot weldability as compared with the comparative steel sheets.
TABLE 30
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.033 0.02 0.22 0.013 0.006
0.0045
0.043
--
D 0.002 0.01 0.09 0.009 0.005
0.0026
0.029
Ti: 0.0029
Nb: 0.011
B: 0.0012
E 0.003 0.01 0.14 0.011 0.004
0.0029
0.031
Ti: 0.033
______________________________________
TABLE 31
__________________________________________________________________________
Properties
Tensile
Roll Surface roughness YS TS shearing Resist-
dulling
Ra SSr
SGr Rmv/
(kg/
(kg/ El force ance to
Steel
method
(.mu.m)
S value
(%)
(.mu.m.sup.2)
Rmp mm.sup.2)
mm.sup.2)
(%)
.sup.-r
L.D.R.
(kg/mm.sup.2)
DOI
galling
Remarks
__________________________________________________________________________
C shot blast
1.5
0.33 43 1060
1.33
19 34 45 1.3
2.07
352 84 4 Compar-
ative
Example
C shot blast
1.4
0.32 41 1090
1.44
19 34 45 1.3
2.06
345 83 4 Compar-
ative
Example
C laser
1.5
0.21 47 2840
1.13
19 34 45 1.3
2.36
483 94 1 Example
D shot blast
1.2
0.43 40 2120
1.50
16 28 51 1.9
2.32
341 85 3 Compar-
ative
Example
D laser
1.2
0.21 48 3840
1.08
16 28 51 1.9
2.50
453 97 1 Example
E shot blast
0.9
0.32 42 2250
1.38
15 29 52 2.1
2.34
350 84 4 Compar-
ative
Example
E laser
1.0
0.08 49 4160
1.04
15 29 52 2.1
2.56
448 96 2 Example
__________________________________________________________________________
EXAMPLE 16
Table 33 shows a dulling method for sking pass roll, kind of plating and surface roughness and properties of the plated steel sheet having a chemical composition as shown in Table 32. As seen from Table 33, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Rmv/Rmp>1 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting, resistance to galling and spot weldability as compared with the comparative steel sheets.
TABLE 32
______________________________________
C Si Mn P S N Al Ti Nb
______________________________________
Steel
0.001 0.02 0.08 0.008
0.008
0.0018
0.044
0.016
0.008
______________________________________
TABLE 33
__________________________________________________________________________
Surface roughness of Deep Tensile
Roll plated steel sheet draw-
Resist-
shearing
dulling Ra SSr
SGr ability
ance to
force
method Kind of plating
(.mu.m)
S value
Rmv/Rmp
(%)
(.mu.m.sup.2)
(L.D.R.)
galling
DOI
(kg/mm.sup.2)
__________________________________________________________________________
Example
laser
Zn electroplating
1.2
0.14 1.13 47 2060
2.24 1 94 438
Example
laser
Zn electroplating
1.2
0.19 1.17 46 2850
2.26 1 96 443
Example
laser
Zn--Ni alloy
1.4
0.16 1.08 48 3620
2.27 1 94 439
electroplating
Compar-
shot blast
Zn electroplating
1.3
0.38 1.38 42 1860
2.06 5 75 352
ative
Example
Compar-
shot blast
Zn electroplating
1.1
0.38 1.44 41 2240
2.01 4 85 348
ative
Example
Compar-
shot blast
Zn electroplating
1.3
0.34 1.27 44 3810
2.04 5 81 339
ative
Example
__________________________________________________________________________
EXAMPLE 17
Table 34 shows a chemical composition of a cold rolled steel sheet used, and Table 35 shows a dulling method for skin pass roll, and surface roughness and properties of the steel sheet. As seen from Table 35, the cold rolled steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Ra.times.Lmv.gtoreq.50, Rmv/Rmp>1 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting, phosphatability, resistance to galling and spot weldability as compared with the comparative steel sheets.
TABLE 34
______________________________________
Steel
C Si Mn P S N Al X
______________________________________
C 0.035 0.02 0.22 0.019 0.006
0.0041
0.045
--
D 0.003 0.02 0.18 0.009 0.006
0.0022
0.039
Ti: 0.029
Nb: 0.009
B: 0.0008
E 0.002 0.01 0.16 0.008 0.004
0.0021
0.036
Ti: 0.034
______________________________________
TABLE 35
__________________________________________________________________________
Tensile
shear-
Surface roughness Properties ing
Roll S YS TS Resist-
force Phos-
dulling
Ra val-
Rmv/
SGr Lmv
SSr
(kg/
(kg/
El ance to
(kg/ phat-
Steel
method
(.mu.m)
ue Rmp (.mu.m.sup.2)
(.mu.m)
(%)
mm.sup.2)
mm.sup.2)
(%)
.sup.-r
L.D.R.
galling
mm.sup.2)
DOI
ability
__________________________________________________________________________
C shot
1.2
0.32
0.82
1310
33.5
55 19 34 46 1.3
2.01
5 413 82 5 Com-
blast par-
ative
Ex-
ample
C shot
1.2
0.38
0.86
1640
39.3
54 19 34 46 1.3
2.05
5 408 84 5 Com-
blast par-
ative
Ex-
ample
C laser
1.3
0.21
1.08
3220
69.2
48 19 34 46 1.3
2.32
1 451 96 2 Ex-
ample
D shot
2.0
0.27
0.94
370
20.3
52 16 29 51 1.8
2.36
4 402 83 5 Com-
blast par-
ative
Ex-
ample
D laser
1.9
0.21
1.21
2170
63.6
45 16 29 51 1.8
2.59
1 421 94 1 Ex-
ample
E laser
1.9
0.19
1.12
3200
71.5
47 16 29 50 2.2
2.53
1 461 97 1 Ex-
ample
__________________________________________________________________________
EXAMPLE 18
Table 37 shows a dulling method for sking pass roll, kind of plating and surface roughness and properties of the plates steel sheet having a chemical composition as shown in Table 36. As seen from Table 37, the plated steel sheets according to the invention satisfying 0.3.ltoreq.Ra.ltoreq.2.0, S.ltoreq.0.25, 2,000.ltoreq.SGr.ltoreq.30,000, Ra.times.Lmv.gtoreq.50, Rmv/Rmp>1 and SSr.gtoreq.45 exhibit excellent press formability, distinctness of image after painting, phosphatability, resistance to galling and spot weldability as compared with the comparative steel sheets.
TABLE 36
__________________________________________________________________________
C Si Mn P S N Al Ti Nb B
__________________________________________________________________________
Steel
0.002
0.01
0.11
0.009
0.005
0.0015
0.032
0.011
0.005
0.0011
__________________________________________________________________________
TABLE 37
__________________________________________________________________________
Surface roughness of Deep Tensile
Roll plated steel sheet draw-
Resist- shearing
Phos-
dulling Kind of
Ra Rmv/ SGr Lmv
SSr
ability
ance to force phat-
method plating
(.mu.m)
S value
Rmp (.mu.m.sup.2)
(.mu.m)
(%)
(L.D.R.)
galling
DOI
(kg/mm.sup.2)
ability
__________________________________________________________________________
Example
laser
Zn electro-
1.3
0.13 1.08 2440
60.4
48 2.26 1 93 481 1
plating
Example
laser
Zn--Ni alloy
0.8
0.17 1.12 3040
70.1
47 2.21 1 96 471 1
electro-
plating
Example
laser
Zn--Fe alloy
1.9
0.18 1.20 2130
63.6
45 2.32 1 92 432 1
electro-
plating
Compar-
shot
Zn electro-
1.4
0.36 0.94 860
30.6
52 2.06 4 75 425 5
ative blast
plating
Example
Compar-
shot
Zn electro-
1.1
0.38 0.86 1760
40.3
54 2.00 5 85 436 5
ative blast
plating
Example
__________________________________________________________________________
As mentioned above, according to the invention, the regular surface roughness pattern is given to the surface of the cold rolled or plated steel sheet and factors thereof are controlled to given levels, whereby cold rolled steel sheets and plated steel sheets having improved press formability as well as excellent phosphatability, resistance to galling and spot weldability can be produced.
Claims
1. A cold rolled steel sheet having an improved press formability, characterized in that said steel sheet has a surface roughness pattern satisfying a center-line average surface roughness (Ra,.mu.m) of 0.3-2.0 and a regularity parameter (S) in at least one direction of not more than 0.25 showing a regularity of surface roughness represented by the following equations: ##EQU6## wherein Xi is a distance between peaks of convex portions at the surface of the steel sheet.
2. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000.
3. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000 and a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50.
4. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000 and a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1.
5. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000 and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
6. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000, a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50, and a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1.
7. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m) of 2,000-30,000, a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50, and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
8. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000, a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1, and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
9. The cold rolled steel sheet according to claim 1, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000, a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50, a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1, and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
10. A plated steel sheet having an improved press formability, characterized in that said steel sheet has a surface roughness pattern satisfying a center-line average surface roughness (Ra,.mu.m) of 0.3-2.0 and a regularity parameter (S) in at least one direction of not more than 0.25 showing a regularity of surface roughness represented by the following equations: ##EQU7## wherein Xi is a distance between peaks of convex portions at the surface of the steel sheet.
11. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000.
12. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000 and a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50.
13. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000 and a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1.
14. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000 and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
15. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000, a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50, and a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1.
16. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m) of 2,000-30,000, a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50, and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
17. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000, a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1, and a mean area ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
18. The plated steel sheet according to claim 10, wherein said surface roughness pattern further satisfies a mean area per one convex portion at center plane of surface roughness (SGr,.mu.m.sup.2) of 2,000-30,000, a product of center-line average surface roughness (Ra,.mu.m) and mean concave distance (Lmv,.mu.m) of not less than 50, a ratio of mean concave radius (Rmv,.mu.m) to mean convex radius (Rmp,.mu.m) of more than 1, and a mean ratio of convex portions at center plane of surface roughness (SSr, %) of not less than 45.
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- Cahiers D'Informations Techniques de la Revue de Metallurgie, vol. 80, No. 5, May 1983, pp. 393-401, Paris, Fr. J. Crahay, et al; "Gravure de la Rugosite des Cylindres de Laminoir Par Impulsions Laser".
Type: Grant
Filed: Dec 19, 1986
Date of Patent: Oct 4, 1988
Assignee: Kawasaki Steel Corporation (Kobe)
Inventors: Saiji Matsuoka (Chiba), Takashi Obara (Chiba), Kozo Tsunoyama (Chiba), Shunichi Tsugawa (Chiba), Shigeru Kobayashi (Chiba), Toshio Ichida (Chiba)
Primary Examiner: John J. Zimmerman
Law Firm: Balogh, Osann, Kramer, Dvorak, Genova & Traub
Application Number: 6/944,679
International Classification: B21D 5300;
